Taking a dose of 6 mg of caffeine per kilogram of body weight has almost no meaningful impact on how much weight a young man who rarely consumes caffeine can lift in a single repetition of bench press or squat, even if the change is statistically detectable.

Taking 6 milligrams of caffeine per kilogram of body weight before a workout can increase the number of repetitions a person can perform to failure during bench press and squat exercises at 70% of their maximum strength, based on measured effect sizes in young men who rarely consume caffeine.

Taking 4 mg of caffeine per kilogram of body weight, whether in gum or pill form, increases the maximum strength and power output during bench press and squat exercises in men who regularly train with weights, compared to taking a placebo.

In young men who rarely consume caffeine, performance on a one-rep max bench press test improves even when they take a sugar pill instead of caffeine, suggesting that expectations or psychological factors can enhance strength output.

Taking caffeine supplements for six weeks while doing strength training does not lead to measurable improvements in maximum strength, endurance, or body fat and muscle mass in men who exercise regularly, even though their muscles may become slightly thicker.

In young males, whether someone is regularly strength-trained or just casually active does not change how much acute caffeine improves muscular endurance, jump height, or one-rep max strength.